Internal combustion engines, both reciprocating and rotary engines, burn fuel to generate power. The combustion process produces an ongoing stream of hot combustion gases. The chemical composition of the stream of hot combustion gases is toxic to human ingestion. Under some conditions, the chemical composition of the hot combustion gases coming from an internal combustion engine is further combustible, and potentially explosive. The heat in the hot combustion gases must be removed from the engine on an ongoing basis in order to maintain a suitable operating environment in which the engine can operate.
To the extent the engine is mounted in an open air environment outside any enclosing structure, the exhaust gases can be vented into the open surroundings around the engine optionally through a scrubbing device and/or a sound attenuation device. However, in many applications, internal combustion engines are housed in relatively closed spaces, such as in engine compartments of land-based motor vehicles, in engine compartments of smaller watercraft, or in effectively totally enclosed quarters of e.g. ocean-going ships. Venting exhaust gases into the environment immediately surrounding the engine in such enclosing environments is unacceptable considering toxicity of such gases, considering combustibility of such gases, and considering heat content of such gases.
Accordingly, it is common practice to mount a ducted exhaust system to such engines, to duct the gases and heat away from the engine, to a safe location where the gases and heat can prudently be vented to the ambient open-air environment. Such ducted exhaust system can be as simple as a tubular pipe connected to an exhaust passage on the engine, leading to a safe venting location. In the alternative, the exhaust system can be quite elaborate in terms both of ducting of the gases and/or passing the gases through additional processes such as through a catalytic converter and/or through a muffler, before finally venting the resultant gases to the open air. Typically, the more sensitive the environment within which the engine is operating, or the more powerful the engine, the more elaborate and/or more sophisticated the exhaust system.
This invention relates to exhaust systems designed for high performance internal combustion engines, recognizing that the concepts utilized in the invention apply as well to exhausting hot gases generated by other sources. Accordingly, it is contemplated that the teachings here, and the claims which follow, will be construed as applying to such other heat sources to the extent the apparatus and methods disclosed here apply to such heat sources.
More specifically, this invention relates to exhaust systems, and especially to manifold pipe assemblies, and manifold pipe clusters in such exhaust manifold assemblies and exhaust systems. Such pipe assemblies, pipe clusters, manifold assemblies, and exhaust systems are used for collecting and disposing of heat and hot gases received from a source of heat and hot gases. Such heat and hot gases are commonly generated in large quantities by high performance internal combustion engines, for example engines capable of developing 350 or more horsepower, such as 1000 horsepower, 1500 horsepower, 2500 horsepower and more with which exhaust apparatus of the invention is suitably used.
Tubular metal manifold pipes are commonly mounted to exhaust passages on the engine to convey heat and exhaust gases away from the engine, and away from the engine compartment or other actual or functional enclosure in which the engine is disposed. Such manifold pipes receive the gases and heat expelled from the engine during exhaust cycles of the respective combustion chambers. Combustion gases and unburned fuel, along with the associated heat, are expelled from the engine through one or more exhaust passages. When a particular combustion chamber is in the exhaust stage of chamber operation, the piston or rotary vane, or other containment structure containing the combustion, forces the exhaust gases out of the combustion chamber through one or more such exhaust ports. Opening and closing of the exhaust ports may be regulated by, for example, exhaust valves in a four cycle engine. During an exhaust cycle of such four-cycle engine, the exhaust valves are lifted to open the exhaust ports through which the gases can escape. When a given exhaust cycle is finished, respective exhaust valves are returned to their closed positions.
Many engines contain or comprise multiple combustion chambers, namely cylinders, which may be aligned in one or more rows or other arrangements, each combustion chamber having its own exhaust requirements and corresponding exhaust apparatus for receiving, conveying, and treating exhaust gases. In high performance engines, individual exhaust manifold pipes are typically assigned to respective individual combustion chambers. Typically, the multiple manifold pipes, associated with multiple respective combustion chambers, are secured to each other at ends of the manifold pipes disposed away from the engine exhaust passages. The ends of the multiple manifold pipes are mounted to a manifold mounting bracket at the engine. The manifold mounting bracket has receiving apertures suitably sized, configured, and positioned to receive the respective manifold pipes in suitable orientation for alignment of the bracket receiving apertures and the manifold pipes with corresponding exhaust passages of the engine. Open pipe ends are, for example, inserted into the apertures in the manifold mounting bracket and are secured to the bracket such as by welding closed those portions of the apertures disposed outwardly of the manifold pipes.
The manifold mounting bracket is mounted securely to the engine by e.g. mounting bolts which extend through corresponding mounting holes in the mounting bracket, and which are turned into threaded holes in the engine. Such mounting brings the manifold bracket receiving apertures and the open ends of the manifold pipes into alignment with respective exhaust passages of the engine. Such alignment creates sealed continuous paths for flow of exhaust gases from the combustion chambers, through the exhaust passages of the engine, through the receiving apertures of the manifold bracket, and through the manifold pipes of the exhaust system, and thus away from the engine.
The engine exhaust passages are typically short, cylindrical apertures leading from respective combustion chambers, through respective exhaust ports, toward outside ambient environment.
The manifold bracket thus serves as an interface, mating the intake ends of the manifold pipes with the exhaust passages of the engine. The plurality of manifold pipes thus connected to the engine are sometimes referred to as a manifold pipe cluster.
In a multiple-cylinder engine, distal outlet ends of multiple ones of the manifold pipes may be received in common into an intake end of an exhaust pipe, which collects exhaust gases from two or more of the manifold pipes, and further conveys the exhaust gases and heat away from the engine. When so combined with an exhaust pipe downstream of the manifold pipe cluster, the combination assembly is generally referred to as an exhaust manifold assembly. Typically, a given multiple cylinder engine may have as few as one exhaust pipe, up to as many exhaust pipes as the engine has cylinders. The exhaust manifold assembly, in combination with any other components used therewith, such as catalytic converter, muffler, tail pipe, etc., defines the exhaust system.
Exhaust gas temperatures at the manifold mounting bracket can be greater than 1000 degrees Fahrenheit. High temperature of the exhaust gases is desirable for high power output from the engine, but places a high degree of stress on the manifold pipes. Namely, excessively high temperatures at especially the intake ends of the manifold pipes can lead to premature failure of conventional exhaust manifold assemblies, compromising the ability of the exhaust manifold assembly to remove the heat and exhaust gases from the engine and engine compartment. Such failure commonly comprises a hole in one or more of the manifold pipes, or in a joint between a manifold pipe and another element of the exhaust system. Exhaust gases can then escape from the exhaust manifold assembly through such holes.
As engine designers develop ever more powerful engines, exhaust gas temperatures at the engine exhaust passages tend to increase in association with the increase in power. Accordingly, while suitable designs are known for tolerating gas toxicity and combustibility in the exhaust systems of lower power engines, designers of exhaust systems are faced with an ongoing process of developing exhaust systems, and especially the manifold clusters which must tolerate increasingly higher temperatures coming out of the exhaust passages, operative to receive such higher temperature exhaust gases at the engine exhaust passages.
One known method of handling the thermal stresses imposed by the hot exhaust gases is to fabricate the manifold pipes with materials which resist failure at the operative high exhaust gas temperatures.
However, material selection as a solution to temperature tolerance is limited in that few materials exhibit the set of necessary properties tolerant of the high operating temperatures; and such materials tend to be costly. In addition, material selection does not provide mechanisms for rapid dissemination and dissipation of the heat from the manifold cluster sufficient to provide suitable use life for the manifold cluster.
While material selection plays a significant role in designing manifold pipes, material selection alone does not provide a cost effective solution to rapid heat dissipation in existing high performance environments. Indeed, known conventional cost-effective materials are susceptible to failure at the high temperatures associated with current high performance engine conditions when transfer of heat out of the exhaust system depends entirely on flow of the hot gases through the exhaust system pipes in combination with conductive and convective transfer of heat from outer surfaces of the pipes to a gaseous surrounding environment.
Conventionally-used exhaust pipe materials are based, separately, on steel and tungsten. However, as engine design progresses, developing higher power output, greater volumes of exhaust gases are developed, at temperatures that may well be higher than currently known or projected temperatures, at the inlet ends of the manifold pipes. Thus, relying on increasingly more sophisticated materials to handle the hot exhaust gases is not a preferred solution. Further, high performance materials such as tungsten can undesirably drive up the cost of the exhaust system.
Rather, it would be desirable to provide alternate exhaust technology for handling exhaust gas heat wherein the alternate technology has the potential for further cost effective development to accommodate increases in volume and/or temperature of exhaust gases as new, more powerful, internal combustion engines are developed.
To effect higher rates of heat transfer from the manifold pipes, it is known to surround a manifold pipe with a second, outwardly disposed cooling jacket pipe and to pass a respective cooling liquid such as water through the jacket chamber between the cooling jacket pipe and the manifold pipe.
Jacketed pipe cooling, with liquid between the manifold pipe and an outwardly disposed cooling jacket pipe is known in especially marine engine applications. The use of jacketed cooling is a step forward in exhaust technology in that the rate of heat transfer to liquid e.g. water is potentially greater than the potential for removing heat using gaseous air surrounding the hot manifold pipes as the heat receiver, because of the higher specific heat of water. Superiority of liquid e.g. water as a cooling medium, as opposed to air, is well known. By adopting water jacket cooling, one can potentially provide a much wider range of cooling capacities than with air-medium cooling, by controlling the incoming water temperature and volume of water flowing through the jacket, as well as other jacket parameters.
However, even with conventional liquid-cooled jacketing, users experience only limited service life from currently available exhaust manifold assemblies at high engine performance conditions, after which one or more of the jacketed manifold pipes fails, or a joint fails, leaking exhaust gases or water ahead of the outlet end of the exhaust pipe. The invention herein provides exhaust systems, and especially manifold pipe assemblies and exhaust manifold assemblies, having significantly greater use lives in such use environments than conventional water-jacketed exhaust systems.
It is known that satisfactory operation of a jacketed cooling exhaust system requires an ongoing flow of cooling liquid (e.g. water) through the cooling jacket chamber. The function of the flowing water is to collect heat from the manifold pipes and to transport the heat away from the pipes, thus reducing the effective operating temperatures of the manifold pipes; and correspondingly reducing mechanical stresses that accompany high temperature operations. But, as indicated above, conventional water jacketed exhaust manifolds do not fulfill the anticipated potential for use life of water jacketed manifold pipes in high performance environments.
The inventors herein have discovered improved designs for liquid jacketed manifold pipe assemblies and for exhaust manifold assemblies. While choosing to not be bound by theory, the inventors believe that failure of conventional water jacket designs is associated with inadequate distribution of water flow inside the cooling jacket chamber. The inventors further believe that the inadequate distribution of liquid flow leads to vaporization of the cooling water in certain areas or zones of the jacketed, water-carrying chamber. Such vaporization of cooling water in the cooling jacket chamber creates water vapor.
The cooling capacity of water vapor is far less than the cooling capacity of liquid water. In addition, water vapor can become trapped in the cooling jacket chamber whereby the inability of the vapor to flow through the chamber with the liquid water and exit the water jacket cooling chamber is attended by a corresponding inability to remove the desired amounts of heat from the affected portion of the water jacket cooling chamber, as well as inability to maintain ongoing flow of cooling water through that portion of the jacketed chamber.
In such instances, the overall temperatures of the manifold pipes rise, and/or hot spots may develop in the pipes, wherever there is vapor or where the vapor is trapped. As the pipes heat up in the hot spots, the metals at those spots expand more than at desirably cooled portions of the pipes, exerting excessive mechanical stresses on the jacketed pipe assembly at such hot spots, resulting in premature pipe failure. For example, repeated expansion and contraction of the pipe and jacket combination under e.g. internal gaseous pressure created by vaporization of the liquid in the cooling jacket can quickly fatigue the metal at the stressed locus, causing a rupture of the metal such as at a joint between sections of the inner manifold pipe.
To contain the cooling fluid within the jacket, the outer jacket pipe must be sealed about the inner manifold pipe at a leading edge of the cooling chamber proximate the engine exhaust passage, between the manifold pipe and the jacket pipe, thus to fabricate the closed jacketed cooling chamber. Under use conditions, the jacket pipe is generally significantly cooler than the manifold pipe. Thus, the jacket pipe material expands less than the inner, hotter manifold pipe. As the inner manifold pipe becomes hotter than the jacket pipe, the manifold pipe expands more than the jacket pipe, placing mechanical stress on the joint, namely the seal between the manifold pipe and the jacket pipe proximate the manifold bracket. Where sufficient temperature gradients exist, such mechanical stress may be sufficiently great to induce premature failure at e.g. such fabricated mechanical joint.
In a first family of embodiments, the invention comprehends a manifold pipe assembly for receiving hot gases from a heat source, and conveying such hot gases from the heat source toward a lower temperature environment. The manifold pipe assembly comprises a manifold pipe having a first inlet end and a first outlet end, and a length between the first inlet end and the first outlet end, the manifold pipe defining a gas path for conveying hot gases from the first inlet end to the first outlet end; a jacket pipe disposed outwardly of, and encompassing, the manifold pipe along a portion of the length of the manifold pipe. The jacket pipe has a second inlet end disposed toward the first inlet end of the manifold pipe, and a second outlet end disposed toward the first outlet end of the manifold pipe. The jacket pipe is closed about and secured to the manifold pipe at the second inlet end of the jacket pipe, thereby to form a cooling chamber between the manifold pipe and the jacket pipe, the cooling chamber having a closed inlet end. The manifold pipe assembly further comprises an inlet pipe providing liquid communication into the cooling chamber. A closed end chamber portion of the cooling chamber is defined between the inlet pipe and a face of the cooling chamber disposed toward the first end of the manifold pipe. The inlet pipe is sufficiently close to the inlet end of the cooling chamber in combination with the closed end chamber portion being suitably configured as to maintain sufficient flow of cooling liquid at the inlet end, into and through the closed end chamber portion, to preclude development of localized hot spots on the manifold pipe adjacent the cooling chamber when cooling water is routinely passing through the cooling chamber during routine operating conditions of the pipe assembly.
In some embodiments, the jacket pipe has an inside diameter at least 0.12 inch, preferably at least 0.25 inch, greater than the outside diameter of the manifold pipe.
Preferably, the cooling chamber has a depth measured between an outer diameter of the manifold pipe and an inner diameter of the jacket pipe, and a ratio of the depth of the cooling chamber to the outside diameter of the manifold pipe, at locations away from the inlet end of the cooling chamber, of about 0.05/1 to about 0.3/1, more preferably about 0.1/1 to about 0.25/1.
In preferred embodiments, the second inlet end of the jacket pipe is spaced e.g. displaced a substantial distance, for example about 0.5 inch to about 3 inches, preferably about 0.75 inch to about 2 inches, from the first inlet end of the manifold pipe at the locus of closest approach.
In some embodiments, the manifold pipe assembly includes, as a relatively enlarged cross-section portion of the jacket pipe, an accumulation reservoir as part of the cooling chamber proximate the second inlet end of the jacket pipe, the accumulation reservoir being effective to increase residence time of cooling liquid in the cooling chamber at the accumulation reservoir.
Preferably the distance between the inlet pipe and the face of the closed end chamber portion is no more than about 0.5 inch, and is preferably about 0.12 inch to about 0.38 inch, optionally about 0.19 inch.
In preferred embodiments, in routine hot gas transfer operation, the manifold pipe exhibits temperature-related color differentiation indications at an outer surface thereof between the first end of the manifold pipe and the second inlet end of the jacket pipe.
Typical exhaust elements of the invention, such as the manifold pipe assemblies, exhaust systems, and the like are well suited for use in combination with internal combustion engines designed and configured to develop significant power levels, such as at least 350 horsepower, for example 1000 horsepower, 1500 horsepower, 2500 horsepower, and more.
Preferred embodiments of the manifold pipe assembly include an accumulation reservoir having a second depth at least 1.2 times as great as the first depth. The accumulation reservoir provides for increased residence time of the cooling liquid adjacent the inlet end of the cooling chamber, compared to the relative residence time of the cooling liquid at respective portions, of equal longitudinal dimensions, along the length of the cooling chamber and away from the accumulation reservoir, thus to provide enhanced cooling capacity precisely at the most useful location along the length of the manifold pipe.
In some embodiments, the jacket pipe, and thus the cooling cavity, including the accumulation reservoir, are disposed toward but spaced from the first inlet end of the manifold pipe.
In preferred embodiments, the ratio of the length of the accumulation reservoir to the outside diameter of the manifold pipe is about 0.3/1 to about 2/1, preferably about 0.6/1 to about 1.5/1.
The accumulation reservoir preferably has ratio of length to maximum depth of about 0.5/1 to about 15/1, preferably about 4/1 to about 10/1.
In some embodiments, the inlet end of the jacket pipe is joined to an outer surface of the manifold pipe at a joint having an approach angle of about 70 degrees to about 110 degrees, preferably about 80 degrees to about 100 degrees, and extends away from the outer surface of the manifold pipe along an arcuate path, thereby enabling the jacket pipe to flex according to thermal stresses placed on the jacket pipe while retaining acceptable levels of stress at the joint.
In preferred embodiments employing the accumulation reservoir, the inlet pipe is sufficiently close to the inlet end of the cooling chamber, optionally in combination with the closed end of the chamber being suitably configured, as to maintain sufficient flow of cooling liquid at the inlet end, into and through the closed end chamber portion, to preclude substantial vaporization of cooling water at the closed end chamber portion under routine operating conditions of the pipe assembly.
Also in preferred embodiments employing the accumulation reservoir, the inlet pipe is sufficiently close to the inlet end of the cooling chamber in combination with the closed end chamber portion being suitably configured as to maintain sufficient flow of cooling liquid at the inlet end, into and through the closed end chamber portion, to preclude development of localized hot spots on the manifold pipe adjacent the cooling chamber when cooling water is routinely passing through the cooling chamber during routine operating conditions of the pipe assembly.
The invention further comprehends an exhaust manifold assembly for receiving hot gases from a heat source and for conveying such hot gases from the heat source toward a lower temperature environment. The exhaust manifold assembly comprises a manifold bracket for mounting to the heat source, the manifold bracket having a plurality of apertures extending therethrough; a manifold pipe cluster comprising a plurality of jacketed manifold pipe assemblies, inlet ends of the manifold pipe assemblies being received in gas-tight securement into respective ones of the apertures in the manifold bracket; and an exhaust pipe, receiving outlet ends of the manifold pipe assemblies in gas-tight securement at an inlet end of the exhaust pipe, the exhaust pipe receiving hot gases from the manifold pipe assemblies and directing the hot gases away from the heat source.
Each jacketed manifold pipe assembly comprises a manifold pipe having a first inlet end and a first outlet end, and a length between the first inlet end and the first outlet end, and defining a closed conveyance path, open on the respective ends, for conveying hot gases from the first inlet end to the first outlet end, a jacket pipe disposed outwardly of, and encompassing, the manifold pipe along a portion of the length of the manifold pipe. The jacket pipe has a second inlet end disposed toward the first inlet end of the manifold pipe, and a second outlet end disposed toward the first outlet end of the manifold pipe. The jacket pipe is closed about and secured to the manifold pipe at the second inlet end of the jacket pipe, thereby to form a cooling chamber having a closed inlet end, between the manifold pipe and the jacket pipe. Each jacketed manifold pipe assembly further comprises an inlet pipe providing liquid communication into the cooling chamber, a closed end chamber portion of the cooling chamber being defined between the inlet pipe and a face of the cooling chamber disposed toward the first end of the manifold pipe. The inlet pipe is sufficiently close to the inlet end of the cooling chamber in combination with the closed end chamber portion being suitably configured as to maintain sufficient flow of cooling liquid at the inlet end, into and through the closed end chamber portion, to preclude development of localized hot spots on the manifold pipe adjacent the cooling chamber when cooling water is routinely passing through the cooling chamber during routine operating conditions of the exhaust system.
In some preferred embodiments, the second inlet end of the jacket pipe is joined to an outer surface of the manifold pipe at a joint having an approach angle of about 70 degrees to about 110 degrees, and extending away from the outer surface of the manifold pipe along an arcuate path, thereby enabling the jacket pipe to flex according to thermal stresses placed thereon while retaining acceptable levels of stress to the joint.